Limited excretion of the persistent chlorinated hydrocarbon pesticide DDT and its metabolites play a major role in bioconcentration of DDT in the food chains leading to man. The major form of DDT excreted in the urine in man, other mammals, and some fish is the acetic acid derivative, DDA. The structure of this compound indicates that it might be eliminated via the well studied PSP-PAH transport system of the kidney. Further, its low excretion suggests that reabsorption may be more important than secretion. If this should be the case, it would be possible to increase net DDA excretion with appropriate inhibitors of the organic acid system and to lower the pesticide burden of the body. This hypothesis will be evaluated in three steps: 1) characterization of the kinetics of DDA influx and efflux from the kidney in vitro and in vivo, 2) analysis of the effect of DDA on the renal transport of other organic acids, and 3) examination of the effect of probenecid and similar pharmacological agents which alter excretion of other organic acids on DDA elimination.